Pressure balancing tub and shower valves are generally used in commercial or public buildings and lately in residential homes. Typically, a pressure balancing valve for a shower, bathtub or combined bathtub and shower is mounted inside the wall and provides water to the shower head or bathtub outlets. Usually the valve is controlled by a single handle that rotates from off to full cold to mixed hot/cold to full hot positions without volume control. Due to changing water demand throughout a home or building plumbing system, the water pressures in the hot and cold supply lines are constantly fluctuating. Pressure increases or decreases can cause unpleasant changes in water temperature or, in extreme cases, can cause scalding. With wide use of manual fast closing valves and electronically controlled solenoid valves, which can cause sudden pressure changes in supply lines, there has been an increased demand for pressure balancing valves. Pressure balancing valves are intended to provide a steady hot/cold water mix ratio regardless of the changing pressure in the supply lines.
There are two types of pressure balancing valves in use in the plumbing industry. The first is the spool and sleeve type and the second is the diaphragm type. Both of these valves utilize the same principle. The pressure balancing mechanism is placed in the constantly pressurized part of the valve in front of the mixing assembly. These valves are designed and manufactured for specific applications and must meet performance requirements set forth in American Society of Sanitary Engineering (ASSE) Standard No. 1016-96. In the diaphragm type of pressure balancing valve, the pressure balancing mechanism is usually contained within a removable cartridge seated within the valve.
The diaphragm type pressure balancing valve usually contains a pressure balancing cartridge made from two molded cartridge halves which separate the hot and cold water passages with the help of a diaphragm. Hot and cold water poppet valves are connected to the diaphragm positioned between the cartridge halves. The poppet valves control the flow of water through a controlling orifice within each water passage. The function of the pressure balancing valve is to provide equal outlet pressures regardless of the hot and cold inlet pressures when water is flowing. The diaphragm/poppet valve assembly reacts to pressure variations. When the pressure increases on one side, the poppet valve assembly moves toward the lower pressure side due to the unbalanced forces. This movement on the higher pressure side reduces the gap between the poppet valve and the seat in the controlling orifice, thus causing an increase in the pressure drop at the controlling orifice. On the lower pressure side, the gap between the poppet valve and the controlling orifice seat increases, causing a reduction in the pressure drop at the controlling orifice. The pressure balancing cartridge also contains damping chambers which serve to slow down the movement of the poppet valve assembly and prevent unnecessary oscillation. The poppet valve assembly moves until the pressures on the two sides of the diaphragm are equal and the pressure in the damping chambers is equal with the outlet pressure.
It is desirable that a pressure balancing valve have the characteristics of a large stroke, short response time, high sensitivity to pressure changes and as a result of this, good temperature control. The stroke defines the range of movement of the poppet valves within the pressure balancing cartridge and defines the maximum flow that the poppet valve will allow through the controlling orifice. The bigger the stroke, the more water flow that can be delivered under normal operating conditions. The response time of the valve is how fast the valve reacts to pressure fluctuations or failure in the supply lines. An important function of the pressure balancing valve is to reduce the flow of hot water quickly upon cold water pressure failure in order to prevent any user discomfort. The valve must reduce the hot water flow under 0.5 GPM within five seconds (per ASSE 1016-96).
The pressure balancing mechanism relies on the action of inlet water pressure on the diaphragm to properly move the poppet valves. The valve sensitivity relates to required inlet pressure differential needed to move the diaphragm and operate the poppet valves. With the introduction of new "low-flow" shower heads, higher back pressures created in the balance chamber, which reduces pressure drop through the control orifices, thereby requiring a more sensitive pressure balancer valve. Most types of valves meet the required performance standards with higher flow rates (3-5 GPM). However, under present Federal law, water through a shower head is restricted to a maximum of 2.5 GPM at 80 psi, and 2.2 GPM and lower flow rate restrictors are widely in use. The valve's sensitivity to pressure changes also relates to its ability to control the temperature of the water delivered to the user. Highly sensitive valve can detect slight pressure changes and adjust itself to maintain the user set mix of hot and cold water ratio.
To address the problem of valve sensitivity and increase responsiveness to pressure variations in low flow environments, various pressure balancing valve configurations have been attempted in the industry. One of these configurations combined the diaphragm type valve's superior responsiveness with the spool & sleeve type valve flow control mechanism. The sensitivity of this valve was increased partially with the introduction of an unbiased, un-reinforced rolling diaphragm. Further improvement was made by removing the O-rings from the damping chambers.
While there are benefits from this configuration, these types of valves have a very high manufacturing cost. The two cartridge halves which make up the pressure balancing cartridge must be aligned perfectly in order to allow for friction free movement of the poppet valve/diaphragm assembly. The poppet holes for each cartridge half have to be machined with very tight tolerances for plastic parts. In addition, two precisely placed alignment holes need to be bored. The hot and cold poppet valves which sit within these poppet holes must be made from one metal piece and must also meet close tolerances in diameter and circular run-out. Finally, the radial clearance within the controlling orifices and damping chambers, between the poppet valve and poppet hole, has to be minimal. These tight tolerances and their associated production difficulties can complicate the manufacturing process as well as result in an unacceptably high manufacturing reject rate.
Other prior art introduces a diaphragm-type pressure balancing valve. Hot and cold water enter the pressure balancing cartridge through hollow poppet valves. Instead of being connected to the poppet valve, the diaphragm is connected to a special housing which contains the flow controlling orifices. The different hot and cold water outlet pressures force the diaphragm/controlling orifices assembly to move and eventually equalize the outlet pressures. The potential problem with this design is the two O-ring seal between the poppet valves and the controlling orifice housing. This seal must maintain proper lubrication. As soon as the lubricant washes away, the increased friction alters the responsiveness and reduces the sensitivity of the valve requiring higher pressure differentials in operation.
Still another prior art valve attempts to address the previously described valve's manufacturability problems. This valve places an O-ring on the poppet valve in the inlet channel which gives the opportunity to increase the radial clearance between the poppet valve and the poppet hole in the flow controlling orifice. On the hot water side, in the case of cold water pressure failure, this O-ring seals against the flow controlling orifice seat. Unfortunately, this type of valve fails to eliminate many of the typical manufacturing problems. The two cartridge halves' poppet holes still need to be machined to exacting tolerances. The one piece metal poppet valve (incorporating both the hot and cold poppet valves) requires close tolerances in diameter and circular run-out. Finally, the radial clearance between the poppet valve and the poppet hole in the damping chamber is still critical for proper temperature control and proper cold water failure performance. While this assembly is more flexible in terms of misalignment tolerances between the cartridge halves, it can still require costly secondary manufacturing operations. The increased clearance within the damping chambers further negatively effects the valve temperature controlling ability.
In view of the presently available valves described above, it must be concluded that there is a need for an improved pressure balancing valve which addresses the drawbacks of existing pressure balancing valves.